Which of these describes an example of a keystone species that scientists should make efforts to protect?

A. More than 1,000 newly hatched wood frog eggs in a forest ecosystem.

B. A gopher tortoise that provides a home to more than 300 different species of animals in its burrow.

C. A nonnative population of lionfish living on a coral reef in Florida that have no natural predators.

D. A population of mistletoe plants that are parasitic because they depend on other trees and plants in the ecosystem in order to get what they need to survive.